A study by Martha Bailey, Brad Hershbein and Amalia Miller assigns an earnings differential to the effects of access to birth control pills. Bailey and colleagues say such access has helped narrow the income gap between men and women. Findings also indicate that the pill had the greatest economic benefits for women with average IQ scores. The study, reported in an NBER working paper, is slated to be published in the July 2012 American Economic Journal: Applied Economics.